Reenforcement



Sept. 29, 1936. R. F. voGT 2,055,129

REENFORCEMENT Filed June 29, 1954 2 Sheets-Sheet 1 R, F. VOGT REENFORCEMENT Filed June 29, 1954' Sept. 29, 1936.

Patented Sept. 29, 1936 UNITED STATES REENFORCEMENT Robert F. Vogt, Milwaukee, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application June 29, 1934, Serial No. 733,062

7 claims.

This invention has to do with the adding of strengthening parts to plate structures which have been weakened by the cutting away or omission of plate material therefrom for purposes of providing an opening in the structure. For instance, in tanks, boilers, tubes and plate metal shells for various kinds of apparatus it is a com-r mon practice to cut away or omit plate material for the purpose of providing an opening, such as a manhole, in the structure, and where the provision of such holes has resulted in an undesirable weakening of the structure reenforcing flanges have heretofore been employed in an endeavor to overcome, or at least to diminish, the weakening eifect of the holes. It is a well known fact, however, that such reenforcing flanges as heretofore employed were not capable of completely restoring the original strength of a plate structure which had been weakened by a hole therein, such as a manhole, and in many instances such flanges have not only been found to contribute nothing to the ability of the structure to withstand the loads which the structure was intended to carry but, under certain conditions, it has even been found that the ability of the structure to withstand the loads was actually diminished by the reenforcing flange, that is, the weakening effect of the hole was enhanced rather than diminished by the reenforcing flange. These difficulties have been encountered particularly in pressure vessels and other plate metal structures in which the plate material was subjected to tensile stresses in the direction of its plane and in which the length of the stressed plate in the direction of the stresses, was short in comparison with the length of the hole in the same direction.

It is an object of the invention to provide a reenforcement for plate structures which have been weakened by a hole therein, which reenforcement enables the structure to withstand tensile stresses to which it is subjected while in use, substantially as eifectively asif the plate material missing at the hole were present and an integral part of the structure.

It is a further object of the invention to provide a reenforcement for plate structures which have been weakened by a hole therein, which reenforcement eliminates or at least considerably diminishes the disturbing effect of the hole upon the distribution of tensile stresses to which the structure is subjected while in use, and which reenforcement produces a substantially uniform distribution of such stresses in the plate struc- 55v ture.

A further object of the invention is to provide an improved connection between a metal plate having an opening therein and a reenforcing flange for said metal plate.

These and other objects and advantages of the 5 invention will be apparent from the following description. A clear conception of embodiments of the invention and of the operation of a device constructed in accordance therewith, may vbe had by referring to the drawings accompany- 10 ing and forming a part of this speciiication, in which like reference charactersY designate the same or similar parts in the several views.

Fig. l is a front view of a plate having a rectangular hole at its center, the upper half of the 15 ligure showing the plate in unstressed condition and the lower half of the ligure illustrating schematically and probably deformation of the plate under tension if the plate is not reenforced.

Fig. 2 is a section on lineI II-II of Fig. 1.

Fig. 3 is a front view of a plate having a rectangular hole at its center and a reenforcing flange securedthereto. Corresponding to Fig. 1 the upper half of Fig. 3 shows the plate in unstressed condition, and the lower half of Fig. 3 25 illustrates schematically the probable deformation of the plate under tension.

Fig. 4 is a section on line IV-IV of Fig. 3.

Fig. 5 is a front view of a plate having a rectangular hole at its center and being reenforced 30 in accordance with the present invention. Correspondingto Fig. 1 the upper half of Fig. 5 shows the plate in unstressed condition, and the lower half of Fig. 5 illustrates schematically the n probable deformation of the plate under tension. 35

Fig. 6 .is a section on line VI-VI of Fig. 5.

Fig. 7 is a view of a shell for a grinding mill for cement or the like, the shell having a plurality of manholes and being rcenforced at the manholes in accordance with the invention.

Fig. 8 is an enlarged view in the direction of' arrow A in Fig. 7, showing the llange and cover for one of the manholes in the shell.

Fig. 9 is a section on line IX-IX of Fig. 8.

Fig. 10 is a section on line X-X of Fig. 8.

Referring to Figs. 1 and 2 lof the drawings and more particularly to the upper half of Figure 1, the reference character I indicates a plate of uniform thickness, extending between blocks 2 and 3, the blocks being shown in dotted lines 50 merely to indicate some suitable means for placing the plate under tension in the direction of its plane. 'I'he plate I has contact with the right block 2 along line 4 and with the left block 3 along line 5, and it should be understood that in of the hole extend parallel to the right and left lines of contact 4 and 5, respectively, and so that the longitudinal edges 8 and 9 of the hole extend parallel to the longitudinal edges I9 and II, respectively, of the plate. The surface of the plate is marked with a number of gauge lines which may be aixed by painting or in any other suitable manner and which extendparallel tothe lines of contact 4 and 5 when the plate is in unstressed or unloaded condition. The gauge lines on the unstressed plate are equally spaced longitudinally of the edges I9 and II, the space between two adjacent gauge lines being indicated by the reference character S. It will be seen that, if no hole were cut into the plate and tension would be applied to the plate by separating the blocks 2 and 3 from each other in parallel rela-` tionship, the parallel relationship of the gauge lines would not be disturbed by the consequent elongation of the plate. The only change to be noted, apart from the transverse contraction of the plate in accordance with Poissons ratio, would be that the gauge lines in the stretched plate are spaced from each other somewhat farther than in the unstretched plate but the increased spacing would be the same between any two adjacent gauge lines and anywhere between the longitudinal edges I@ and II of the plate.

Referring now to the lower half of Figure 1 this part of the gure illustrates schematically the conditions resulting from the application of tension to the perforated plate I by separating the blocks 2 and 3 from each other in parallel relationship as indicated above, the transverse contraction yof the plate as determined by Poissons ratio being neglected in this gure. As a result of the tension applied through the blocks 2` and 3 the longitudinal edge II of the plate Will elongate in accordance with the separation of the blocks, and assuming that the side edge 9 of the hole is spaced from the side edge II of the plate a suicient distance, the elongation of the plate along the edge l I will be uniform throughout its length, that is, the gauge lines will be spaced equally along the edge II of the elongated plate and the individual spaces between adjacent gauge lines at the elongated edge I I, which have been indicated by S', will be proportionally larger than the spaces S of the gauge lines on the unstretched plate. In the middle between the longitudinal edges 8 and 9 of the hole a longitudinal axis of symmetry has been'indicated by the reference numberal I2, and it will'be' noted that along this axis the plate material between the contact line 4 and the right edge of the hole, and the plate material between the contact line 5 and the left edge of the hole is not, or at least not appreciably elongated due to the separation of the blocks 2 and 3. The relative` spacing of the gauge lines above and below the hole along the axis I2 Will therefore be the` same, or nearly the same, in the stretched plate as in the unstretched plate. Considering the elongation of the longitudinaledge 9 of the hole it will be noted that the right and left edges 6 and 'I of the hole intersect the side edge 9, if the plate is not stretched, at right angles, but that in the stretched plate this right angle relation does no longer exist, but that the right and left edges assume a more or less arcuate shape. The ratio of elongation of the side edge 9 between the points of intersection with the right and left edges B and 1 is greater than the ratio of elongation of the side edge II of the plate and, consequently, the relative spacing of the gauge lines along edge 9 is also greater than the relative spacing of the gauge lines along edge I I. In the middle between thelines of contact 4 and 5 a transverse axis of symmetry, indicated by I3, has been shown, and

the gauge line coinciding with said transverse axisof symmetry remains undisturbed by the application of tension and the consequent elongation of the plate. As the distance of the gauge lines from the axis I3 increases in the direction of axis I2 the gauge lines become more and more distorted, and the distortion reaches a maximum inthe regions adjacent to the right and left,

edges 6 and 1 of the hole; from there on the distortion gradually subsides and practically disappears at the right and left lines of contact 4 and 5. vIt will be seen that the distortions of the gauge lines are due to the presence of the hole in the plate, and the nature of the distortions indicates that the portions of the plate adjacent to the longitudinal edges of the hole and particularly the portions adjacent to the corners of the hole are subject to stresses far greater than those in the rest of the'plate. It Will further be noted that the normal' distances of the edges 6 and'1 from the Contact lines 4 and 5, respectively, have a considerable influence upon the extent to which the gauge lines kwill be distorted, that is, that the distortions of the gauge lines will be greater if'the edges 6 and 1, in the unstretched plate, are in close proximity to the contact lines 4 and 5 than in the case where the Contact lines 4 and 5, in the unstretched plate, are spaced from the edges 6 and I a suflicient distance so as to be out ofthe range of disturbance. In other words, if the lengthof. the unstretched plate Vin the direcbeen shown but with a reenforcing flange secured thereto. The reenforcing ange surrounds the hole and has longitudinal strap or tie portions I4 and I5 extending along the longitudinal edges 8 and 9 of the hole, and transverse beam portions I6 and I'I extending along the transverse edges E and 'I of the hole. The longitudinal straps i4 and I5 are each made of suitable material and are properly dimensioned in such amanner as to elongate under tension'in the direction of axis I2 at the same ratio as the plate material which has been cut out at one side of the longitudinal axis I2 would elongate under the same tension. The beam portions I 6 and It are of the same thickness, perpendicularly of the plate, as the strap portions I4 and I5 but the height ofv each beam,rtransversely of axis I3, Varies along said axis, and on axis I2 the height of each beam is considerably greater than the width of one of the strap portions I4 or I5 in the direction of the transverse axis I3. This 4.5 tion of the Vstresses issrnall in comparison with ff- Shape `of the beam portions I6 and I'I has been selected in order to make the beams particularly adapted to resist deformation due to tensile stresses in the strap portions I4 and I5. The reenforcing ange is secured to the plate in a conventional manner by two Vwelded seams, one extending along the transverse edges I5 and 'I and the longitudinal edges 8 and 9 of the hole and the other extending along the outer circumference of the flange. The gauge lines on the plate Ir shown in the upper half of Fig. 3 are the same as those shown in the upper half of Fig. 1 but in Fig. 3 the gauge lines have been shown dotted where they are covered by the reenforcing frame.

The lower half of Fig. 3 illustrates schematically the conditions resulting from the application of tension to the reenforced plate by separating the blocks 2 and 3 from each other as explained in connection with Fig. 1. The relative spacing of the gauge lines along the longitudinal edge II of the plate in Fig. 3 is the same as in Fig. 1 and the same reference character S. has beenused to indicate the increased spacing of the gauge lines along edge I I in comparison with the normal spacing S of the gauge lines indicated in the upper half of Fig. 3. The relative spacing of the gauge lines along the longitudinal axis I2 at the rightand left of the transverse edges 6 and 'I of the hole differs materially from that shown in Fig. 1 on the unreenforced plate. Within the range of the beam portions I6 and I1 of the flange, that is, on those portions of the plate which lie directly behind the beam portions I6 and I'I the spacing and parallelism of the gauge lines is the same, or practically the same, in the stretched plates as in the unstretched plate because the beams and the plate portions behind them are united by the inner and outer welded seams into solidbodies which will not, or at least not appreciably, elongate due to the application of tension to the plate. In the space between contact line 4 and the outer edge of beam portion I6, and in the space between contact line 5 and the outer edge of beam portion I'I, however, the relative spacing of the gauge lines along axis I2 is larger than the relative spacingof the gauge lines along edge II. Along the longitudinal edge 9 of the hole the relative spacing of the gauge' lines is the same as along the side edge II of the stretched plate because the ratio of elongation of edge 9 is equal to the ratio of elongation of edge I I due to the reenforcement of the edge 9 by the strap I5 which, as stated, has been made to elongate at the same ratio as the plate material missing at the hole between the axis I2 and edge 9 would elongate, if present; and for obvious reasons that ratio of elongation is the same as the ratio of elongation of edge I I. It will be noted that the gauge lines are considerably distorted in the regions adjacent to the outer edges of the beam portions I6 and I'I and that theplate portions in these regions are subject toy stresses far greater than those prevailing in the rest of the plate. In other words, the disturbing effect of the hole upon an equal distribution of the stresses in the plate as demonstrated in connection with Fig.

1 is not eliminated but merely altered by the use of the reenforcement shown in Fig. 3. Under certain conditions this alteration may be a change for the worse in that the stress concentration in the vicinity of the hole reaches higher values with a reenforcement than without a reenforcement, and in that case the reenforced plate would naturally fail sooner than the unreenforced plate. It may be said, therefore, that if it is desired to eliminate or at least to diminish the weakening effect of a hole upon the tensile strength of a plateA of uniform thickness, the problem involved consists primarily in avoiding as nearly as possible stress concentrations in the unreenforced portions of the plate.

Referring now to Figs. 5 and 6 of the draw ings, these figures show how .the plate I shown in Figs. 1 and 2 may be reenforced according to the invention in such a manner that no` stress concentration occurs in any portion of the plate if the plate is placed under tension by separating the blocks 2 and. 3 from each other as explained in connection with Figs. 1 and 2. The upper half of Fig. 5 shows the plate in unstressed condition and a reenforcing flange similar to the one shown in Fig. 3, but in contrast to Fig. 3 the reenforcing flange of Fig. 5 is secured to the plate only by a singlev welded seam extending along the -transverse edges 5 and 'I and the longitudinal edges 8 and 9 of the hole. The welded seam along the outer edge of the flange, shown in Fig. 3, has been omitted in Fig. 5, and in order to indicate the loose relation between the plate and the major part of the iiange more clearly the flange has been shown in Fig. 6 with a low shoulder at the side facing the plate, the shoulder projecting from the flange near itsinner edge and extending all around the hole. In all other respects the flange shown in Fig. 5 is identical with the one shown in Fig. 3, that is, the strap or tie f portions I4 and I5 are made of a suitable material and are properly dimensioned in 'such a manner that they elongate under tension in the di-v rection of axis I2 at the same ratio as the plate material which has been cut out of the plate would elongate under the same tension ii it were present and an integral part of the plate. The beam portions It and I'I in Fig. 5, like those shown in Fig. 3, are of the same thickness perpendicularly of the plate as the strap portions I4 and I5 but the height of each beamportion, transversely of the axisflS, varies along said axis and is a maximum on axis I2 in order to make the beams particularly adapted to resist deformation dueto tensile stresses in the strap portions M and I5. In other words, the beam portions I IS and I'I in Fig. 5 are designed to takeup all those tensile stresses which would fall upon the plate material missing at the hole, if it were present. and to transmit those tensile stresses upon the strap portions I4 and I5 without being appreciably deected while performing this function. The relative spacing of the gauge lines lon the plate in the upper half of Fig. 5 is the same as in the upper halves of Figs. 1 and 3, and the portions of the gauge lines which are covered by the flange have been shown dotted asin Fig. 3.-

Considering the conditions resulting from the application of tension to the reenforced plate of Fig. 5 by separating the blocks 2 and 3 as explained in connection with Fig. 1,.it will be noted from the lower half of Fig. 5 that the relative spacing of the gauge lines along theedge II of the plate is uniform and that the spaces S' between adjacent gauge lines along the elongated edge II are larger than the spaces S between adjacent gauge lines along the unstretched edge I0, the elongation of the individual spaces being proportional to the total elongation of the plate. The

relative spacing of the gauge lines along the axis.

I2 between the contact line 4 and the edge 6 of the hole and between the Contact line 5 and the edge 'I of the hole is also uniform because the plate material along the mentioned portions of axis I2 is free to elongate independently ofthe beam portions I6 and I1. Finally, the relative spacing of the gauge lines along the elongated edge 9 of the hole is uniform and the same as the relative spacing of the gauge lines along edge II of the plate for the same reasons which have been set forth above in connection with the elongation of edge 9 in the lower half of Fig. 3. It follows that the spacing of the gauge lines along axis I2 above and below the hole, which is uniform as stated, must also be equal to the spacing of the gauge lines along edge II, so that a parallel relationship of the gauge lines is insured throughout the stretched plate just in the same manner as in a plate which has no hole and which is subject to the same tension as the plate shown in Fig. 5.

The reenforcing flange shown in Fig. 5, due to its particular design and manner of attachment, as will be seen, restores to the plate I with the hole in it the original tensile strength which the plate would have Without the hole. In order to obtain this result it is not absolutely necessary that the Welded seam which connects the frame with the plate be placed along the edge of the hole as shown in Fig. 5. It is possible to place the welded seam anywhere between the edge of the hole and the outer edge of the flange or even let the seam coincide with the outer edge of the frame and still maintain a uniform stress distribution anywhere between the seam and the outer edges of the plate. It should be noted, however, that in moving the transverse portions of the welded seam which have been shown in Fig. along the edges B and 'I of the hole, away from those edges, that is nearer to the contact lines 4 and 5, the design of the reenforcing frame must be appropriately changed so that the whole portion of the frame which lies between the transverse seams elongates under tension at the same ratio as the longitudinal side edges of the plate elongate. The improved results of a reenforcement embodying the invention may be said to depend on the condition that the width of the connection between the frame and the plate at those sides of the hole which extend transversely to the direction of the stresses is short in directions radially of the hole, and on the condition that the flange is designed in such a manner that, under tension, its elongation between those connections equals or substantially approaches the elongation which would result from the same tension on the plate material required to fill the space between said connections.

The principles of the invention set forth hereinbefore have been applied to the construction of the grinding mill shell shown in Fig. 7. The shell has the general shape of a round hollow cylinder and suitable means, not shown in the drawings, are employed in its operation to support the shell at its opposite ends for rotation about its longitudinal axis. The shell has an` outer sheet metal wall I8 and the inner surface of the wall I8 is covered with a lining I9 as is usual and well known in the art. A number of stiffening rings 20 are placed around the shell and are rigidly secured thereto, preferably by welding. In certain of the spaces between the stifliening rings manholes are provided in the shell, and reenforcing flanges 2I are placed around the Inanholes and secured to the shell, the reenforcing flanges also serving as seats for manhole covers 25 which are retained thereon by means of cross bars 22 and bolts 23 carrying nuts 24. A lining 26 corresponding to the lining I9 of the sheet metal wall I8 is secured to the inner surface of each manhole cover 25 by means of bolts and nuts 21.

The openings in the Wall I8 which form the manholes are of elliptical shape and the reenforcing flanges 2I have a correspondingly elliptical shape but are dimensioned and secured to the wall I8 in accordance with the principles Yof the invention set forth hereinbefore. The reenforcing flanges are all alike, and in the following reference will be made particularly to the fiange shown at A in Fig. 7. The portion of the flange projecting over the edge of the hole in wall I8 towards the center of the hole has a shoulder 28 extending down into the hole, the shoulder beingv shaped along an ellipse concentric with the ellipse 32 of the edge of the hole in wall I8, and the side of the shoulder facing the vertical side of the hole in wall I8 is equally spaced all around from the latter so as to provide a groove for the deposition of Welding material 29 which unites the flange with the wall I8. At the side of shoulder 28 which faces the center of the hole a seat 30 is formed for the cover 25 and a cloth inserted rubber packing 3I is placed between the cover 25 and the seat 30. The cover is held in position by the bolts 23 which extend through the cross bars 22 and by the nuts 24 which are drawn up against the cross bars. The height of the flange, above wall I8, is greatest above the seat 38 and gradually decreases radially of the hole as best shown in Figs. 9 and l0. As is also shown in these figures, a low abutment 35 is formed on the side of the flange facing the wall I8 of the shell, the abutment engaging the wall portions closely adjacent to the edge of the elliptical hole in the wall. The entire surface of the flange between the abutment 35 and the periphery or outer edge of the ange is slightly spaced from the surface of wall I8, the deposit of welding material 29 forming the only rigid connection between the flange and-the wall I8. At its periphery the flange is slightly reenforced by a crowning 36 which extends all around the flange as shown in Fig. 8. Y

The vertical inner surface of the flange which extends upwardly from the seat 30 follows an ellipse 33 concentric and coplanar with the ellipse 32 of the hole in wall I8, the ellipse 33 'being radially spaced from the ellipse 32 ,the same amount all around, or in other words, the ellipse 33 has major and minor diameters which are each the same amount shorter than the major and minor diameters, respectively, of the concentric ellipse 32; that is, the major diameter of ellipse 33 is the same amount shorter than the major diameter of ellipse 32 as the minor diameter of ellipse 33 is shorter than the minor diameter of ellipse 32. The peripheral or outer edge of the flange is also defined by an ellipse concentric with the ellipse 32 of the holevin wall I8, but in contradistinction to the ellipse 33 of the inner. edge the ellipse of the outer edge which has been indicated in Fig. 8 by the reference numeral 34, has a major diameter which differs from the major diameter of ellipse 32 a substantially greater length than the minor diameter of', ellipse 34 differs from the minor diameter of ellipse 32; the major diameter of ellipse 34 exceeds the major diameter of ellipse 32 for a length which is substantially greater than the length for which the minor diameter of ellipse 34 exceeds the minor diameter of ellipse 32. The result of the different relations of the ellipses 33 and 34 to the ellipse 32 is that'the cross-sections of the flange along its major diameter, which areshown in Fig. 10, are larger than the cross-sections ofthe flange along its minor diameter, which are shown lin Fig. 9. The cross-sections of the flange along its minor axis, as shown in Fig. 9, are preferably dimensioned so that the combined cross-sectional area of the flange and the welded seam, at each side of the major axis of the fiange, is equal or substantially equal to the area of a rectangle whose long side equals the arcuate distance between the center and the edge of the hole in a plane through the center of the hole at right angles to theaxis of the shell, and whose short side equals the thickness of wall I 8, provided that the flange and welding material are of substantially the same material as the Wall I8. Comparing the cross-sections of the flange taken on the minor axis (Fig. 9) with those taken on the major axis (Fig. 10), it will be noted that the inner side of each cross-sectional figure, that is, the side facing the center of the hole has been indicated by the reference numeral 31. The sides 31 of all cross-sectional figures are substantially perpendicular to the plane of wall I8 and are otherwise alike. Considering the moment of inertia which each cross-section has with respect to its respective side 31 it will be noted that the moments of inertia of the cross-sections taken on the major axis of the flange are substantially greater than the moments of inertia of the crosssections taken on the minor axis of the flange. The portions of the flange between the vertices of the ellipses 33 and 34 on the major axis are, therefore, particularly adapted to withstand the bending stresses to which they are subjected due to tensile stresses in the side portions of the flange, that is, in the portions of the flange laterally of the major axis, particularly in the vicinity of the minor axis. The manhole flange shown in Figs. 8, 9 and 10 functions substantially in the manner explained in connection with Fig. 5 to eliminate the disturbing effect of the hole in wall I8 upon the distribution of tensile stresses in said wall, acting in the direction of the axis of the shell. The same considerations apply, of course, to the other manhole flanges shown in Fig. 7.

Referring again to the manhole shown at A in Fig. 'l it should be noted that the manhole is placed in relatively close proximity to one of the stiffening rings 29, and this particular relation of the stiffening ring to the manhole is especially liable to cause a highly unequal distribution of axial tensile stresses in the wall I8. For the reasons set forth in connection with Fig. 5, however, such unequal distribution of axial tensile stresses will be effectively counteracted by the reenforcement through the flange described in connection with Figs. 8, 9 and 10.

While in the foregoing the invention has been explained in connection with rectangular and elliptical holes only, it is equally well applicable to holes of any other shape, for instance circular holes. Likewise, the structures which have been described hereinbefore in connection with the figures are illustrative only as to the conditions construction herein shown and described, for various modifications within the scopewof the claims may occur to persons skilled inthe art.

lt is claimed and desired to secure by Letters Patent:

1. The combination of a'plate member having an ellipticalfhole in it and being subject to tensile stresses principally in the direction of the major4 axis of said hole, with an velliptical reenforcing flange concentric with said hole, said reenforcing flange having an elliptical inner edge equally spaced all around from the edge ofsa'id hole and an elliptical outer edge, the majordiameter of the ellipse of said outer edge exceeding the major diameter of the ellipse of said hole a greater length than the minor diameter of' the ellipse of said outer edge exceeds the minor diameter of the ellipse of said hole, and a deposit of binding material uniting said flange With said plate member along the edge of said hole.

2. The combination set forth in claim 1, in which the major diameter of the ellipse of said inner flange edge is the same amount shorter than the major diameter of the ellipse of said hole as the minor diameter of the ellipse of said inner flange edge is shorter than the minor diameter of the ellipse of said hole.

3. The combination of a plate member having an elliptical hole in it and being subject to tensile stresses principally in the direction of the major axis of said hole, with an elliptical reenforcing flange concentric and coaxial with said hole and connected to said plate member by a welded seam along the edge of said hole, said reenforcing flange having an elliptical inner edge equally spaced all around from the edge of said hole, and an elliptical outer edge whose major diameter exceeds the major diameter of the ellipse of said hole a greater length than the minor diameter of the ellipse of said outer edge exceeds the minor diameter of the ellipse of said hole, and the crosssection of said flange at each side of the center of said hole and in the direction of the minor diameter of the latter being substantially equal in area to a rectangle whose short side equals the thickness of said plate member and whose long side equals half the distance between diametrically opposed points of the ellipse of said hole measured in the plane of said plate member in the direction of the minor axis of said hole.

4. A plate member having a hole in it and a reenforcing flange secured thereto for the purpose of substantially restoring to said plate member its original tensile strength in at least one principal direction, said reenforcing flange comprising a pair of beam portions extending transversely to said principal direction at opposite sides of the center of said hole and being secured to said plate member solely near edge portions of said hole extending transversely to said principal direction, and tie portions extending in said principal direction and connecting said beam portions with each other, said beam and tie portions being constructed, mounted and arranged relative to each other and to said plate member so that said beam portions do not appreciably bend under bending stresses set up therein between their connections with said plate member and said tie portions by tensile stresses acting upon said plate member in said principal direction, and so that elongation of said tie portions under the tensile stresses transmitted thereto by said beam portions prevents tensile stresses acting upon said plate member in said principal direction from concentrating in said plate member in the vicinity of said hole.

5. A combination as set forth in claim 4, in which each of said beam portions is secured to said plate member solely by a Welded seam along the edge of said hole.

6. A combination as set forth in claim 4, in which each of said beam portions is secured to said plate member solely by a welded seam along the edge of said hole, and in which said tie portions are directly secured to said plate member by Welded seams extending in said principal d1'- rection.

7. A combination as set forth in claim 4, in which each of said beam portions is secured to said plate member solely by a Welded seam along the edge of said hole, and in which a pair of said tie portions is arranged at opposite sides of the center of said hole and in which each tie portion is directly secured to said plate member solely by a Welded seam along an edge portion of said hole extending in said principal direction.

ROBERT F. VOGT. 

